Potentially Dangerous Arachnids and Insects

Introduction

Note: This article deals only with the poisonous and venomous arthropods, not the ones that spread disease. The purpose of this article is to assist you in determining whether the “bug” or spider you have found is potentially dangerous.

This article covers all of the potentially “dangerous” arachnids (spiders and their kin) and insects found in the United States.

Many people think that “bugs” are out to get them, which is completely untrue. Almost all “bugs” are harmless and are actually beneficial and only a few species are potentially harmful.
One thing to remember about “bugs” is you don’t bother them and they won’t bother you; however, if you need to remove an unwanted insect or spider, place a clear cup over it and slowly slide an index card underneath the cup.
Do not try to pick up the insect or spider, rather learn and observe without touching. All of the arachnids and insects listed here are normally docile and are not aggressive. However, if you try to pick it up, or otherwise disturb it, some of the arachnids and insects will feel threatened and will defend themselves. Some of these defense mechanisms can be painful, or even harmful.

How to use
For a larger picture, click on the thumbnail. For more pictures, click on the More Pictures links. For more information about a particular topic, click on the underlined links listed in the reference section below each topic. Also please check the Guide Page links, as they will have more information about the range, habitat, and typical size of the specific arachnid /insect.If you do not find your specimen listed here, then it is probably not dangerous.
If you are still unsure and would like confirmation, please submit your images
to the ID Request page.
If your specimen is listed below, and you have additional questions, check the General Discussion forum and post your question there.

All of the arachnids and insects shown here bite and sting only in defense, they will not bite/sting unless provoked.

Spiders
Spiders are important controllers of pests and only a very small number of species can or will bite humans even if provoked.
You have a better chance of dying from a bee sting than from a spider bite.
The only spiders in this article that are truly “dangerous” are the Black Widow and the Brown Recluse. Other than those, the bite of most spiders are comparable to a bee sting. If you are ever bitten by any spider, capture it for identification as it can be important in determining the course of treatment.

Orb Weavers - Very common – Extremely important controllers of pests - The chances of getting bitten by any species of orb weaver are slim to noneMore PicturesGuide Page
Most orb weavers can or will not bite humans. The few species that will bite will only do so if squeezed or otherwise provoked. Typical reactions include localized pain with slight redness, which quickly subsides.

Sac spiders - Chiracanthium inclusum - Chiracanthium mildei - Trachelas tranquillus
Several species of sac spiders are suspected of being responsible for most indoor spider bites to humans. Like most spiders, sac spiders typically do not bite unless they are trapped against the skin or provoked. Sac spiders are nocturnal, therefore bites are most likely to occur at night.

Chiracanthium inclusum is native to much of the United States, except for the northernmost states. C. mildei is an introduced species from Europe. As of 1978, it was found throughout much of the Northeast; however, it is likely that it has greatly increased its range since then.
The bite of a yellow sac spider usually results in instant, intense, stinging pain, similar to the sting of a bee or wasp; localized redness; and a burning sensation lasting for up to an hour, with rash and blistering occurring during the next 1-10 hours. There is slight swelling at the site of the bite for a day or two. Sometimes an ulcerated lesion develops at the site of the bite. This ulceration normally heals itself within several weeks.

This spider ranges from New England south to Georgia and Alabama and west to Kansas and Minnesota.
There are records of severe secondary infection associated with the bite, which may result from the spider's propensity for feeding on dead arthropods. Typically, the bite results in redness and some swelling, similar to a bee or wasp sting.

Tarantulas – Will not bite unless provoked – Their venom is no worse than most bee stings; however, some tarantulas can release a cloud of hairs that irritate the mucous membranes of mammalsMore PicturesGuide Page
Tarantulas are huge spiders, with a distinctive, menacing appearance, which has given them an undeservedly sinister reputation. A fact sheet on tarantulas

Black Widow – The bite of the adult female can be fatal - Will not bite unless provoked

Black widows are nocturnal. During the day the female will hide in a secluded corner of her web. At night she will hang upside-down in the web which is built close to the ground.The male black widow is not dangerous. The adult female black widow has a red hourglass (or part of) on the underside of the abdomen. The female black widow may also have red or white marking on the top of the abdomen.
The shape of the female black widow is distinctive and the spider has a smooth, hairless appearance. Female black widows are only aggressive when they are protecting an egg sac, otherwise they will try to flee.
The female black widow has a notorious habit of eating the male after mating, but there are exceptions if the female is already well fed.
This is the most venomous spider in North America, but almost all healthy people who are bitten will recover in a few days. Very few deaths from black widow spider bites are reported in the U.S., but the risk of death from a bite remains.
The bite of a black widow may feel like a pin prick or the victim may feel nothing at all. Two red marks may appear where bitten, along with minor swelling. Pain will become intense within 1 to 3 hours, continuing for up to 2 days, and can spread from a bitten limb into the abdomen or back. Severe cramping or rigidity may occur in the abdominal muscles. The victim may also exhibit other symptoms including nausea, vomiting, shaking, profuse perspiration, and labored speech and breathing, possibly progressing to a weak pulse, clammy skin, unconsciousness, and convulsions. Symptoms often diminish after about a day and are gone after several days. Serious long-term complications or death from a black widow bite are very rare.ReferencesA fact sheet about the Black WidowInformation about the widow spidersA fact sheet on the Black Widow, its bite, habitat, and how to get rid of itInformation about the widow spiders, their bite, symptoms of the bite, web, and life cycle“Commonly Encountered Pennsylvania Spiders” Covers several spiders found throughout the U.S.

Recluse spiders – Genus Loxosceles – Will not bite unless provokedLoxosceles sp.Guide Page
Several species of recluse spiders are found in the U.S.; best known
is the infamous Brown RecluseIf you do not live in any of the colored areas on the maps below, then it is quite unlikely that you have a recluse spider. Recluse spiders are only rarely transported outside of their range on or in furniture, boxes, and plants.
See this map for the distribution of recluse spiders in the U.S.
See this map for the distribution of the Brown Recluse.
The Brown Recluse has uniformly colored legs covered with fine hairs. The legs have no stripes, banding, or spines on them. The abdomen is also uniformly colored. The body of the Brown Recluse is under half an inch in length.
Some species of recluse spiders have a well-defined dark violin-shaped marking on the “head” region of the spider with the neck of the violin pointing toward the abdomen; however this is not a conclusive way to identify a recluse spider. All recluse spiders have six eyes whereas most spiders have eight (this can only be determined with the use of a microscope.) For more information on how to identify a Brown Recluse see this link.
Recluse spiders are nocturnal, therefore most likely encountered at night when they are foraging for food. During the day recluse spiders hide in secluded places.
Little is known about the venom and bite of the lesser-known species of recluse spiders.
“Although there are suspected variations in virulence among the species, all Loxosceles spiders should be considered potentially capable of producing dermonecrosis (skin necrosis) to some extent.” (1)Most Brown Recluse bites result in only a small red mark and heal without serious complications.
An interesting fact is the Brown Recluse cannot bite through clothing because of its small fangs.
The bite of the Brown Recluse is usually painless and many go unnoticed for as long as 2 to 8 hours or the victim may feel a stinging sensation later followed by intense pain. A small white blister develops at the site of the bite, followed by swelling of the area. This swollen area enlarges and becomes red. The site becomes painful and hard to the touch. A necrotic lesion develops and the affected tissue dies and slowly sloughs away exposing the underling tissue. This necrotic ulcer may persist for several months and heals slowly, leaving a sunken area of scar tissue. It is exceedingly hard for a physician to correctly diagnose a "brown recluse bite" based simply on the wound characteristics.
In extremely rare cases, a systemic reaction may occur. Systemic symptoms resulting from a brown recluse bite are kidney failure, black urine (from high levels of hemoglobin in it), and disseminated intravascular coagulation (small blood clots throughout the body).

References Cited1 Vetter, R. S. Arachnids Submitted as Suspected Brown Recluse Spiders
(Araneae: Sicariidae): Loxosceles Spiders Are Virtually Restricted to
Their Known Distributions but Are Perceived to
Exist Throughout the United States J. Med. Entomol. 2005; 42(4): 512-521

Hobo spiderMore PicturesGuide Page
The Hobo spider is native to Europe. In the U.S., it is commonly found in the Pacific
Northwest (See this map).
It is very hard to positively identify a Hobo spider. If you think you have found a Hobo spider take it to a specialist.
“…evidence for hobo spider envenomation causing necrotic ulcers consists of one verified bite in a patient with a pre-existing medical condition known to cause ulcer disease, rabbit model bioassays, and many purported envenomations that could easily be ascribed to other etiologies.” (2)

True Bugs – The larger ones can inflict a painful bite - The chances of getting bitten by any species of true bug are slim, unless you handle one. More PicturesGuide Page
A small number of true bugs feed on the blood of vertebrates; aside from these, only the larger ones can bite humans, but only if handled

Ants, Bees, & Wasps – Order Hymenoptera
In ants, bees, and wasps the stinger is a modified egg-laying apparatus, so only females can give a venomous sting.Bee and wasp stings account for almost all of the deaths by insects and arachnid bites/stings in the U.S.
Ordinarily, Hymenoptera venom will only cause local pain and swelling.
However, some individuals, like me, may be allergic to Hymenoptera stings. An allergic reaction to Hymenoptera stings occurs once the victim becomes sensitized to the venom from a previous sting. The allergic reaction is caused by the immune system, which has now been oversensitized to the venom and releases histamines into the bloodstream. Histamines dilate blood capillaries, causing the skin to appear red and feel warm, and also makes the capillaries more permeable, which allows fluid to escape into the tissues. This causes swelling, which is manifested as rapidly appearing hives, accompanied by severe itching. In a severe allergic reaction called anaphylactic shock, the tissues of the throat swell and the victim may have difficulty breathing and, unless promptly treated, death may resultAnts, bees, and wasps will only sting if stepped on, handled or otherwise provoked.

Africanized honeybees (Killer bees) are more aggressive than ordinary honeybees. They guard a larger area around their hives, become upset more easily by humans and machinery, and respond faster and in larger swarms. They will chase threatening humans and animals for as much as a quarter of a mile. Africanized honeybees are from the southern part of Africa. They were brought to southern Brazil, and have since spread as far north as the southwestern U.S.

Male Cicada Killers are very territorial, and will patrol almost constantly in a small area near a nest, flying at anything passing by.

The female hunts for cicadas and when she finds one she will capture and then sting it. The sting only paralyzes the cicada and the female wasp lays an egg on the cicada and then buries it alive as food for the larva. Females may have multiple underground chambers in a single nest with one larva in each chamber. Female Cicada Killers are not aggressive and will not sting unless grabbed or otherwise provoked.

Moths & Butterflies
Some caterpillars, mainly those of moths, have stinging “hairs” that can cause an irritating reaction when touched.

Saddleback caterpillar

Buck Moth

Io Moth

Puss Caterpillar

Spiny Oak Slug Moth

Hag Moth

Stinging Rose Caterpillar

Hickory Tussock Moth

Family Arctiidae - Tiger Moths

Browntail Moth
An invasive species which, if touched, can cause a rash similar to that of poison ivy. The rash is the result of a toxin in the hairs and the barbed hairs becoming embedded in the skin. In sensitive individuals, the rash may be severe and persist for several weeks. If the hairs are inhaled, respiratory distress may result. In the U.S., the Browntail moth is found in many of the New England states.

Horse fly larvae – If they are handled roughly or trodden upon with bare feet they can inflict a very painful bite, but their venom is not dangerous to humans
Most horse fly larvae are found in water or moist soil. They are fierce predators, capturing their prey with their sharp sickle-shaped mandibles and paralyzing it with an injection of venom. Note: Female horse flies feed on the blood of livestock, humans, and other large mammals and in doing so give a painful bite. Male horse flies feed only on nectar.ReferencesInformation on horse and deer fliesMore information on horse and deer flies

under horse fly larva references does not work for me. In the second link, the first photographed horse fly is Diachlorus ferrugatus, not Chrysops sp. as the article says. Also italicizing the order name, as in under Hymenoptera, is unnecessary.

A question on a very minor point to an outstanding article!
In your short statements on Orb and Jumping Spiders you say
"Most *** can or will not bite humans". Do you mean to say;
"Most *** can not or will not bite humans", and please don't pay
attention to the way i wrote cannot.

When this topic was active I didn't think of its implications for your article. And then there was this eye-opener about a group of spiders not covered here. One other thing I never noticed before: Centipedes and millipedes aren't "Arachnids and Insects", so the title isn't quite accurate.

I realize that this thread is very old, but I thought I'd post my thoughts anyway. First, this is a fantastic article - just had to throw that out there. Second, I was under the impression that Hobos were very aggressive (even known by some as the "aggressive house spider"), and will sometimes attack without provocation. If this is not correct I apologize, but you might want to further research the matter just in case.

Thank you - Below is a quote from the guide page for the Hobo spider:
"The name means "rural, of the fields" from ager- "field" + -estis (an ending that means "of or belonging to," usually referring to a place.)
A common misconception is that agrestis means "aggressive", giving it the name "aggressive" house spider. This spider is not aggressive, and would rather flee than fight, unless it feels threatened without the option to escape. (This misconception is often used to help fuel fears about the potential hazards of this spider.)"
I will add a note about this to my article. Thanks for your input!

Robber flies, family Asilidae, although not apt to bite, produce a VERY painful bite, worse than horse or deer flies (Tabanidae). And I have seen people "Run For Their Lives" because some are huge, can mimic wasps and bees, and are loud. If trapped or handled they, like reduviid bugs, can simply turn and bite the dog-poop out of you! In this regard, I agree another section on painful yet not dangerous (except causing one to run into a tree or into traffic dumbfounded by the pain) arthropods be created.
Harvester ants, Pogonomyrmex spp.: I have had the misfortune of standing in a "pogo" mound (which is actually a bare, flat circle about 3 feet across) and, well, we were camping, so, when ya gotta go... anyway, I ended up with over 20 stings on my lower legs. It was not a good feeling: ILL. Severe headache, increased lethargy, and ecitedness, not to mention the intense dull pain and throbbing of my legs, chills.... I have read that anaphylactic shock is not uncommon. Symptoms subsided overnight (couldn't sleep), totally "cured" after 4 days.
See also my new reply on Pepsis down among Eric's suggestions.

Such projects can't help always being a "work in progress". There is always going to be some other bug that fits your criteria. For example: horse fly larvae will inject a venom into a human if they are handled roughly or trodden upon with bare feet when a human is walking in water. See for comments.

I have now added links to Bugguide pages and to other websites. I have completed the introduction. I still have to change some things though. What do you think? Does anyone have any more ideas or corrections?

After I posted the whole thing about internal links, I realized I hadn't actually tried them out- they work fine with regular html pages, but Troy's software often rewrites the html during the posting process. I tried it every way I could think of and they didn't work in any of the things I had access to, so I deleted as much as I could of what I wrote (I didn't want to be spreading misinformation about how to do things here).

It would seem internal links work in articles, though- so I'm glad you read what I wrote before I gave up and got rid of it.

Looking very good... it's apparent you have put quite a bit more effort and information into it. Thank you for your continued effort; this document will be very important to the various visitors that search the guide.

Brown Recluse Section
About your recluse spiders... The genus Loxosceles is actually comprised of "brown" spiders, rather than "recluse" spiders. The Recluse (or Brown Recluse) is just one species of brown spiders. :)

Also, only the Brown Recluse (L. reclusa) has a potent necrotic venom; the other Loxosceles spp. spider bites, while quite unpleasant, do not have the "significant medical factor" of the L. reclusa. (This is probably what you meant, but the mixup between "recluse spiders" and "brown spiders" makes this point unclear.)

In your brown recluse writeup, you have a slight "numbers" mismatch in one sentence:During the day recluse spiders hide in secluded places.

Additional Links
Wow, you have been scouring all over the net for these, haven't you? For these additional links, I would suggest moving them to the specific/relevant arachnid sections (if applicable). If someone is looking up a specific spider, they might not scroll down far enough to see the additional links. Also, for some spiders, there is a bugguide guide page for it (like the hobo spider (Tegenaria agretis)).

I will move the links up to the relevant part of the article if no one has any objections. I will also change the "recluse" spider and make a note about the brown recluse's venom. Thanks for your help!
Oh, and have I forgotten any important spiders?

This makes me very nervous. The reference was written decades ago for professional exterminators (or at least those studying to become exterminators). There's a very strong disclaimer on the web site begging people not to follow the pesticide recommendations, since the understanding about the effects of pesticides on both insects and the environment (not to mention the laws regarding them) has changed drastically since it was written.

Linking directly to the chapter bypasses the disclaimers and gives the appearance of uncritically endorsing everything in it. If you're going to provide that link to the general public, you really need to give enough context so they won't be misled into trying things that are unsafe and/or illegal.

Good job including the yellow sac spider, however the photo used seems to be more black than yellow. From my experience, all of the ones that I've encountered are actually yellow. I know that there are different species, but I'd like to suggest that a different photo of the spider may be something to consider.

Black Widow: A comma splice, and a typo:Black widows are nocturnal, during the day the will hide in a secluded corner of their web.

You can't use a comma to join two separate, complete clauses. Depending on the relationship between the two you could use a semicolon, a dash or a period.

Recluse spiders: Possible comma splice, omitted word(s):There are several species of recluse spiders, best known is the Brown Recluse

Jumping spiders: Your main point regarding them seems to be that they don't belong in the article at all. Might I suggest a section about harmless species that have gotten a bum rap? At least give some explanation as to why jumping spiders are included but most of the other mostly harmless ones aren't.

A point that could be made is that any bite can lead to a) infection, because arthropods don't brush their mouthparts between meals (ANIMALS!!!), or b) an allergic reaction with possible anaphylactic shock.

Also, the phrase "the temporary appearance of an erythematic region" means nothing to the average, non-medically-trained reader. I can guess that it means simply that there's some redness around the bite for a while. Using technical terminology with people who don't know it may impress some, but most will just skip to the part they understand and miss your point.

Scorpions: No mention of what's dangerous about them (though maybe you just haven't gotten to that part yet).

True Bugs: "The chances of getting bitten by any species of True bug are slim" overlooks the bloodsucking species.

This brings up a philosophical point: I gather this article is really about poisonous and venomous arthropods rather than merely dangerous ones- after all, disease transmission by bloodsucking insects is an astronomically greater danger than spider bites (bubonic plague, malaria, sleeping sickness, etc. kill millions and have changed the course of history on a grand scale). Not that you need to deal with them here- that would be another (huge) article.

Ants: A typo:It is very had to separate the sting and biting ants from the many species of harmless ants.

Fire Ants: A typo:About thirty people a year die form fire ant stings.

Solitary Bees I don't know if solitary bees and wasps have milder stings- I believe the point is that they're far less likely to sting, since they're only protecting themselves and not a whole colony. You're also likely to get stung more times per incident by social bees/wasps because there are more of them attacking you. It might also be good to address the whole "Killer Bee" hype.

Browntail Moth: A typo/omitted word:If the hairs are inhaled respiratory [__?] may result.

All of these criticisms are offered in the spirit of improving an already very good article, not of tearing it down. Believe it or not, I do the same to my own writing, as do most writers. The goal is to be to be merciless to your mistakes without losing faith in your ability as a writer. Hemingway once said that "Every first draft is s[omething very colorful that I'll omit, since this is a family medium...]."

Let me recommend a very useful (if dated) source that I keep running into on Google searches:

Thanks for pointing out all of my stupid mistakes. This article is about only the poisonous and venomous arthropods, not the ones that carry disease. I will try to replace most of the technical terminology with something that most people can understand. I will remove the part about Jumping spiders if no one has any objections. You're right, I haven't gotten to the part about scorpions yet.
As for solitary bees and wasps I got stung by solitary wasp and had only a localized reaction. About two weeks later I got stung by a yellowjacket and had a rather severe systemic reaction and had to go to the ER. Still I am not sure about the venom of solitary wasps and bees being milder than that of social wasps and bees. Maybe an expert can help?
Thanks for all your help. I will fix all of those spelling and grammatical errors as soon as I have time.
Chris

Don't be silly! I wouldn't have spent all that time coming up with suggestions if I didn't think you were worth the effort. As I said in my previous comment, everybody has problems with their first drafts (I lost count of how many times I hit the Preview Comment button last night in preparing my comment).

Possibly the best skill you can teach yourself is how to learn from your mistakes without taking them personally.

As for the solitary bee/wasp issue, I noticed a remark in the Urban Entomology article that many solitary wasps do, in fact, have milder venom. I'm just not sure if it can be safely generalized to solitary bees and wasps as a class. At any rate, I'm certainly not an expert on such things- so my opinions shouldn't be given more weight than those of the real experts here.

I live on a Honeybee farm so I do have some experience on this topic. Somewhere in this mist of posts and replies it is stated that solitary bee and wasps have a milder venom because they have less to protect. While there is some validity to this statment, it is not completely right. Social bees and wasps have less potent venom because of one simple reason, numbers. Social bees often attack in swarms of 2-3 to 30-50, so they rely on a "pain in numbers" strategy. A solitary bee or wasp has one stinger to attack with, so a more potent venom will be more beneficial to the bee or wasp, in terms of iradicating the intruder.

As I've aforementioned, I live on a Honeybee farm and have been stung by Honeybees many, many times and would much rather get stung by them than a Bumblebee.

I also realize that this thread is two years old, so I will be suprised if anyone actually reads this.

This proves that I'm also not an expert. While Bumble bees are social, they live in smaller numbers(a couple of hundred in a colony), and they over winter alone, so while they are alone, they are looking out for Numero Uno, so a stronger venom is necessary.

I would say there is wide variation not only in venom potentcy, but also, and more importantly, in individual reaction to stings and bites. One's immune system has the last word on how a given sting or bite affects the individual. Further, I have heard that the more stings, the more sensitive you become over time; you do NOT develop increased immunity. Dr. Justin Schmidt, the "king of sting," has some very interesting journal articles on this subject.

I just asked my dad about this and he said to tell my own experience. When I was about five years old I was stung by a honey bee and broke out in hives. I went to see an allergy doctor about it and he put me on allergy medication(shots). This went on for three years and I was "cured", Then when I was ten I was stung and my throat closed, I was rushed to the emergengy room and found out that I was in fact still allergic. I was put on shots again but really only became desenseitized when I entered puberty. So there is a form of desensitization, but only occures once a person hits puberty, there is also the fact that my family or I don't swell up and turn red from bee stings

That's not true, when my Mom and Dad started beekeeping they would get stung and react so bad that they had to take there rings off or they(the rings) would cut of circulation to there fingers. But now that they have each been stung many thousands of times, they hardly (if at all) swell up. It IS one of the things that you can be desensitized to.

you both are right. From personal experience, each time a person who is sensitive bee/wasp venom is stung, the reaction typically gets worse. Interestingly, the way this is treated is to inject the individual with minute amount of venom and gradually increase the dose over a period of weeks to months the affected individual is desensitized to the venom and no longer reacts in such a severe manner.
As for the potency of solitary/social venom, I think Eric is right, in that there is a lot of variation in venom potency, and that each individual reacts differently and that it depends on if the person is allergic to the venom.
Personally, from my experience, I think that the venom of solitary wasps is “designed” to cause a lot of pain to the attacker so that the wasp can simply get away. On the other hand, social bees/wasps must stop the attacker before it can damage or destroy the colony’s home, so their stings cause a more severe reaction.

You might want to check out this topic on the General Discussion Forum. One of the references linked to says "Saltids are the most common biting spider in the United States." That sounds like a good reason to include Phidippus. Maybe you could restore that section, but with an explanation that you're including it because it's a frequent biter, but that it's pretty harmless.

Also, you might want to check out this website. The author definitely has strong opinions and possibly a biased perspective- but the site definitely hits all the opposing viewpoints to the conventional wisdom about spider bites.

To our guide pages and/or to other websites with more detailed info? Even as footnotes it would be helpful, I think. On the subject of footnotes, what about some indication of where your information is coming from? Again, goes to credibility.

I just realized that clicking on an image took me to the guide - maybe that should be spelled out in the introduction - kind of "how to use this information and not go into a panic about your mysterious bug or spider"

I appreciate all the work you're putting into this, Chris. We definitely need this article!

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